This invention relates to an improvement in mattress innerspring units and, more particularly, to a means for preventing the tendency of cross helicals to unwind or spin-out from the unit.
Mattress innerspring units are generally formed of a plurality of coil springs positioned standing side-by-side in a plurality of substantially parallel rows. The end or terminal convolutions of the coil springs define the upper and lower surfaces of the unit. Springs adjacent to one another in the same row are interconnected by cross helicals which laced together the coil springs along both their terminal convolutions. The cross helicals therefore extend transversely of the rows of coil springs in both the upper and lower surfaces of the unit. Mattress inner spring units generally include two border wires which extend about the perimeter of the unit. The border wires are normally secured to the upper or lower terminal convolutions of the coil springs at the perimeter of the unit by means of border wire helicals which lace the terminal convolutions and border wires together.
The cross helicals are incorporated into the unit by rotating them spirally about their major axis until they extend across the rows of coil springs, each cross helical interconnecting, i.e., lacing together, a pair of adjacent coil springs in each row along either their upper or lower terminal convolutions. Once the cross helicals are so positioned, they have a tendency to "spin-out", that is, unwind from the innerspring unit. This longitudinal movement of cross helicals is extremely undesirable, resulting in deterioration of the construction of the innerspring unit. A means for preventing cross helical spin-out that is economical and not disruptive of the general methods for assembling innerspring units is greatly advantageous.
It has been the practice to eliminate spin-out by deforming the cross helicals in various manners. Cross helicals have been deformed at their ends by bending the end back upon themselves or forming loops therein, such as is described in U.S. Pat. Nos. 3,006,629 and 2,374,850. Cross helicals have also been distorted at a point along their lengths, such as is described in U.S. Pat. No. 3,685,062.
It has also been the practice to prevent longitudinal movement of cross helicals by providing frictional engagement of the helicals with the coil springs, such as is described in U.S. Pat. Nos. 2,254,106 and 3,653,082.
In spring assemblies which include helical wires disposed between spiral coils which do not lace the coils together, it is known to interconnect the spiral coils and helical wires by means of clips, as described in U.S. Pat. No. 2,052,325. A further known manner of connecting helical wires not laced about terminal convolutions of adjacent coil springs in disclosed in British Pat. No. 10,686. This patent describes an assembly of spiral coils including a helix extending around the periphery and a number of longitudinally extending helices. The longitudinal helices are secured to the periphery helix by clips with two perpendicular threaded sockets to receive the two helices.
It is desirable that cross helicals which extend across the rows of coil springs lacing together adjacent spiral coils be restrained from spinning-out or unwinding from the innerspring unit. It is further desirable to restrain cross helical spin-out by such means that does not increase the cost of construction of an innerspring unit to any appreciable extent and is not disruptive of the generally used methods of construction. It is further desirable to prevent spin-out by a means which is not dependent on deforming the cross helicals because deformations can be decreased in effectiveness upon extending or severe use of an innerspring unit.
It is often desirable to increase the overall firmness of an innerspring unit which is the ratio of resistance provided by the unit per unit load of compressive force applied. Firmness is dependent upon a number of variables particularly coil count (ie number of spiral coils per unit) and the extent of hinging movement between spiral coils. It would be advantageous to increase the firmness of a unit without increasing the coil count and therefore the cost of the unit.
It would also be desirable to eliminate the need for border wire helicals by providing a means for preventing cross helical spin-out which also secures the border wire to the unit, decreasing the cost of construction.
It is therefore an object of the present invention to provide a mattress innerspring construction including a rigid border wire wherein cross helical spin-out is eliminated by providing a restraining means at the end of the cross helicals which prevents them from moving beyond the border wire. It is another object of the invention to provide a restraining means adapted to be mounted at the end of a cross helical and secured to the adjacent border wire to prevent spin-out.
It is a further object of the invention to provide a means for preventing spin-out while increasing the firmness of the innerspring unit. It is also an object to prevent cross helical movement while eliminating the need for border wire helicals to secure the border wires to the unit.